This invention relates to a document illuminating apparatus in general, and in particular, it relates to an illuminating apparatus which is especially useful for evenly illuminating a narrow scanning line used, for example, in document imaging and photocopying apparatuses.
Currently, arrays of green light emitting diodes (LEDs) are used for illuminating documents in some facsimile machines. These LEDs typically emit light at a peak wavelength of 565 nanometers with a spectral width of 60 nanometers. For black and white documents with a sufficiently high contrast, using such green LEDs produces good document images. However, for colored documents, the narrow-spectrum light source from the green LEDs mentioned may not be suitable. For example, with the LEDs mentioned, a light color background on a document may appear darker than expected on an image of the document whereas a dark character printed in a certain color on the document may turn out lighter than expected on the image. As a consequence, the contrast between the character and its background will be significantly reduced. In an extreme case, this reduction of contrast can lead to a loss of information in the final electronic image.